The major objective of this proposal is to describe dietary fat saturation effect upon whole body cholesterol metabolism. Rats will be fed diets containing 40% of calories as a mixture of beef tallow and soybean oil to give a polyunsaturated to saturated fatty acid ratio of 0.33 or 3. Radioactive mevalonate will be injected to be a tracer of endogenous cholesterol. Rats will be killed at intervals of 8 hous to 80 days and cholesterol and cholanoic acids isolated from liver, adipose, muscle, skin, brain, kidney, etc., quantitated and specific radioactivity determined. Cholanoic acids will be identified and quantitated individually. Curves of cholesterol disappearance will be constructed and kinetic models for whole body metabolism devised.